Nodira's apricots were the best in the row, and for three years she sold them at four thousand som a kilo. Then her son, who had begun studying economics, told her she was undercharging. "Raise the price," he said. "You will earn more."
She did not argue. She kept a notebook instead.
For one week she charged five thousand and sold one hundred kilos. The week after she charged six and sold ninety. Then seven, and eighty. Her son was delighted: the price was climbing and the money was climbing with it.
Nodira kept going. At eight thousand she sold seventy kilos, and the week's takings were the same as the week before. At nine thousand she sold sixty, and the takings fell. At ten thousand she sold fifty, and they fell again, harder.
She showed her son the two columns. Every time she added a thousand to the price, ten kilos walked past her stall to the next one. For a while the extra thousand was worth more than the ten lost kilos. Then, quite suddenly, it was not.
"There is a peak in the middle," she said. "Before it, raising helps. After it, raising hurts. Your books tell you to raise the price. They do not tell you when to stop."
Her son went back to the notebook that evening and drew the takings as a curve. It rose, it levelled off, it came down — the same shape he had been drawing in class all year, in a column of his mother's handwriting.